1. Field of the Invention
The present invention relates to a planar microlens array comprising a number of lenses arranged in a two-dimensional array, and a method of manufacturing such a planar microlens array.
2. Description of the Related Art
Planar microlens arrays are incorporated in liquid crystal display panels, for example. One liquid crystal display panel is shown in FIG. 1 of the accompanying drawings. As shown in FIG. 1, the liquid crystal display panel includes a planar microlens array 100 comprising an array of convex microlenses 102 provided on a surface of a base glass plate 101. The convex microlenses 102 are made of an ultraviolet-curable synthetic resin having a high refractive index. The array of convex microlenses 102 is covered with a cover glass plate 103 which is bonded to the array of convex microlenses 102 by an adhesive layer 104 that is made of an ultraviolet-curable synthetic resin having a low refractive index.
A liquid crystal layer 106 is filled between the cover glass plate 103 and a glass substrate 105 spaced from the cover glass plate 103. The glass substrate 105 supports transparent pixel electrodes 107 on its surface facing the liquid crystal layer 106. The surface of the glass substrate 105 Includes areas that are free of the transparent pixel electrodes 107 and carry interconnections and TFTs (Thin Film Transistors) which do not pass applied light. Electrodes 108 which confront the transparent pixel electrodes 107 are mounted on a surface of the cover glass plate 103 that faces the liquid crystal layer 106.
The planar microlens array 100 operates as follows: Applied light is converged by the convex microlenses 102 onto the transparent pixel electrodes (pixel apertures) 107 to brighten an image projected onto a screen.
Presently available liquid crystal display panels have pixel dimensions ranging from about 40 xcexcm to 60 xcexcm. It is expected that the pixel dimensions will be reduced to about 20 xcexcm to 30 xcexcm in the future to meet demands for clearer displayed images.
The smaller pixel dimensions require the convex microlenses 102 to be reduced in size, resulting in a shorter focal length. For efficient utilization of the applied light, it is necessary that the focal point of the convex microlenses 102 be positioned substantially on the transparent pixel electrodes 107. To meet such a requirement, the cover glass plate 103 must be reduced in thickness.
Each of the convex microlenses 102 and the adhesive layer 104 is made of an ultraviolet-curable synthetic resin. The ultraviolet-curable synthetic resin shrinks when cured. The cover glass plate 103 can withstand the shrinkage of the ultraviolet-curable synthetic resin, i.e., can maintain its dimensional stability, when the ultraviolet-curable synthetic resin shrinks, providing that the cover glass plate 103 is thinner, it tends to yield and allow the entire planar microlens array 102 to warp upon shrinkage of the ultraviolet-curable synthetic resin, as shown in FIG. 2 of the accompanying drawings.
It is an object of the present invention to provide a planar microlens array which is resistant to warpage upon shrinkage of an ultraviolet-curable synthetic resin used therewith.
According to an aspect of the present invention, a planar microlens array includes a base glass plate, a cover glass plate, an array of microlenses made of an ultraviolet-curable synthetic resin and disposed between the base glass plate and the cover glass plate, and a film of an ultraviolet-curable synthetic resin disposed on a surface of the base glass plate remote from the array of microlenses.
When the ultraviolet-curable synthetic resins are cured by exposure to ultraviolet radiation, the shrinkage of the ultraviolet-curable synthetic resin of the film is kept in equilibrium with the shrinkage of the ultraviolet-curable synthetic resin of the convex microlenses. Thus, any unwanted warpage of the planar microlens array is minimized in its entirety.
The array of microlenses may comprise an array of convex microlenses made of an ultraviolet-curable synthetic resin having a relatively high refractive index and disposed on a flat surface of the base glass plate, or an array of convex microlenses made of an ultraviolet-curable synthetic resin having a relatively high refractive index and disposed in respective concavities defined in a flat surface of the base glass plate.
The film may be made of a material which is the same as or different from the ultraviolet-curable synthetic resin of the array of microlenses.
The planar microlens array may further include a protective film applied to a surface of the film on the base glass plate for protection of the planar microlens array during shipment or handling.
According to another aspect of the present invention, a method of manufacturing a planar microlens array comprises the steps of shaping an uncured ultraviolet-curable synthetic resin into an array of microlenses between a base glass plate and a cover glass plate, forming an uncured ultraviolet-curable synthetic resin into a film on a surface of the base glass plate remote from the array of microlenses, and simultaneously curing the uncured ultraviolet-curable synthetic resin shaped into the array of microlenses and the uncured ultraviolet-curable synthetic resin formed into the film by exposure to ultraviolet radiation.
The uncured ultraviolet-curable synthetic resin may be formed into the film on the base glass plate by a stamper, a brush, or a spinner.
According to still another aspect of the present invention, a method of manufacturing a planar microlens array comprises the steps of shaping an uncured ultraviolet-curable synthetic resin into an array of microlenses between a base glass plate and a cover glass plate, placing an uncured ultraviolet-curable synthetic resin on a surface of the base glass plate remote from the array of microlenses, laying a protective film over the uncured ultraviolet-curable synthetic resin placed on the surface of the base glass plate, spreading the last-mentioned uncured ultraviolet-curable synthetic resin into a film with a flat surface of a stamper brought into direct contact with the protective film, and simultaneously curing the uncured ultraviolet-curable synthetic resin shaped into the array of microlenses and the uncured ultraviolet-curable synthetic resin spread into the film by exposure to ultraviolet radiation.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when read in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative example.